1,5- and 1,8-dihydroxyanthraquinone, as well as mixtures thereof, are important intermediates in the manufacture of a large number of dyestuffs. One synthetic route to those compounds involves the conversion of the anthraquinone disulfonic acid to the dihydroxyanthraquinone by treatment of the disulfonic acid with Ca(OH).sub.2 and MgCl.sub.2 at a temperature of 215.degree.-230.degree.C (c.f. Lubs, The Chemistry of Synthetic Dyes and Pigments, 1955 Reinhold Publishing Corp., pages 367-368). The mixed 1,5- and 1,8-anthraquinone disulfonic acids can be obtained by sulfonating anthraquinone with 36-40% oleum in the presence of mercury catalyst. The 1,5 isomer can be salted out from the more soluble 1,8 isomer after dilution. In connection with this synthesis, however, the use of mercury catalyst presents the problem of disposing of a mercury-contaminated reaction medium, which disposal is attended by rather serious ecological considerations.
Direct dinitration of anthraquinone, separation of the 1,5- isomer and conversion of the nitro group to the hydroxyl group has not been acceptable since there are produced about 20% of isomeric nitro compounds that are difficult to separate and remove.
It is apparent that one desirous of preparing alphadihydroxyanthraquinones is confronted by the proposition that, in order to obtain a high quality product, it is necessary to use a route that results in an unacceptable environmental impact while, on the other hand, the attempt at a different route results in a mixture of isomers whose resolution is difficult and expensive.